The mechanical properties of the Ni-Fe-based Alloy 718 depend very much on grain size, as well as the strengthening phases, γ' and γ''. The grain structure of the superalloy components is mainly controlled during thermo-mechanical processes by the dynamic, meta-dynamic recrystallization and grain growth. In this investigation, the evolution of the grain structure in the process of two-step blade forging was experimentally and numerically dealt with. The evolution of the grain structure in Alloy 718 during blade forging was predicted using a 2-D FE simulator with implemented constitutive models on dynamic recrystallization and grain growth. The comparison of the simulated microstructure with the actual grain structure of the forged parts validated the prediction of the grain structure evolution. The effect of dynamic recrystallization on the evolution of grain structure is highlighted in this article.
In this study, direct powder rolling was applied to make thin sheets from HDH (hydrogenation and dehydrogenation) powders. Effects of materials and process parameters on tensile properties of sintered sheets are investigated. In the direct powder rolling with two-horizontal counter-rotating rollers, materials parameters including powder size and process parameters such as roll gap, roll speed, and packing height are controlled. With -100mesh Ti powders, CP titanium sheets of a thickness up to 1.5mm and a width up to 300mm were obtained without any rolling defects. Sintering of the rolled strips was performed between 1000°C and 1250°C at 50°C intervals for 1hour to 4 hours. The relative density of the sintered strips was found to be around 85 to 90 percent. After sintering, the complete densification was made by cold rolling, and microstructures and tensile properties were evaluated after annealing treatment at 750°C for 2 hours.
The effect of post weld heat treatment on mechanical properties of friction welded Alloy
718 and SNCRW was investigated. Friction welding tests were carried out at a constant rotation speed
and pressure. Optimum friction condition was found to be the friction pressure of 25kg/cm2, friction
time of 40sec, upset pressure of 80 kg/cm2, and dwell time of 5sec. After friction welding tests, post
weld heat treatments were performed in the temperature range of 500-900°C for 8hrs in order to
investigate the microstructure and mechanical properties of weld joint. Specimens with the post weld
heat treatment at 720°C for 8hrs show optimal mechanical properties. Residual stress of post weld
heat treated specimens was measured to weld joint in the same temperature range. After friction
welding tests on samples with a diameter of 80mm, tensile properties of post-weld-heat-treated and
non-heat-treated samples were compared.
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